This invention relates to railway rolling stock and more particularly to railway trucks, which ride on rails and provide support for car bodies.
Many of the design features of railway trucks have remained the same over the past century, with improvements being made primarily in refinement of individual components and scaling up of the components for carrying higher capacities. A conventional truck comprises a pair of spaced parallel unitary side frames which are supported near their ends on wheel and axle assemblies. A transverse bolster centrally connects the side frames, and the ends of the bolster are supported on helical springs carried in opposed side frame windows. The bolster resiliently supports the car body. Mechanical snubbers are employed to dampen vertical movements of the bolster, and shoes are carried by the bolster and frictionally engage vertical columns on the side frame.
While the prior art is crowded with many suggestions to improve the ride and performance of so-called three piece trucks of the foregoing nature, many problems have remained unresolved, presumably due to characteristics inherent in the design. The side frames, which form rigid connections between the front and rear wheels on each side of the truck, are heavy castings. This necessarily results in a high unsprung weight between the wheels and bolster, contributing to poor riding qualities. The two trucks beneath the car may contribute up to forty percent of the tare weight of the total structure.
A second problem with existing truck designs is unlevel riding qualities under varying speeds, loads and track conditions. One example is a phenomena of rock and roll, in which the car body and trucks may rock from side to side to a dangerous degree.
Another problem is the inability of present designs to maintain a square condition because of the H relation between the side frames and the bolster. The bolster has portions in slidable engagement with columns of the side frame, and these parts tend to wear over a period of time. The design contributes to the problem known as hunting, in which the wheels on one side of the truck may precede the wheels on the other side and cause an erratic ride. The problem may become intensified as the relevant parts become worn.
Finally, conventional railway trucks contain numerous cooperating parts which must be carefully engineered in order to perform in a satisfactory manner, all contributing to cost. Notwithstanding all these problems and more, there has been a reluctance to deviate or make fundamental departures from the current basic design.